The present invention relates to a control circuit. More particularly, it relates to a servo control circuit for controlling the tape drive of a magnetic tape recorder reproduced system.
In the art of magnetic recording, it is important that the speed at which the tape is driven both in recording and in playback be held to a constant value. It is also important, under many conditions, that the speed at which the tape is driven in the playback, or reproduce, mode be the same speed at which it was driven during the recording mode. One technique for accomplishing the latter desideratum is to record a control signal on the tape during the recording process which is to be used in controlling the velocity of the tape during playback. It is, of course, recognized that such machines must be sufficiently flexible to be operated at any one of a number of different selected speeds. Thus such machines may be operated at speeds ranging from 15/16's of an inch per second to 120 inches per second in eight distinct steps. In the industry, there has been set forth a standard set of different frequency control signals for controlling the tape speed at each of the selected speeds. In systems which have been used heretofore, it was recognized that there is a natural frequency response characteristic curve for magnetic tape heads. Traditionally, in order to accomplish the uniformity of output signal, a substantial amount of complex filtering and characterizing are applied to such curves.
Similarly, in previous apparatus, the effective selection from among the numerous tape speeds has entailed a complex system of switching and selection of control circuits.